1. Field of the Invention
The present invention relates to a method of differentiating bottom-fermenting yeast (bottom-fermenting yeast for brewering) and wild yeast.
2. Related Background Art
In the process of brewing of alcoholic malt beverages (beer, low-malt beer and the like), inclusion of wild yeast not used for brewing, such as Hansenula, Brettanomyces and Candida, or Saccharomyces strains not used as brewing yeasts, results in inferior aroma characteristics of the alcoholic malt beverages, and in some cases causes clouding or off-flavor.
It is therefore important, from the standpoint of maintaining and controlling the yeast fermentation properties and the aroma characteristics of alcoholic malt beverages, to rapidly differentiate whether or not yeast detected in the process of brewing of alcoholic malt beverages is bottom-fermenting yeast.
Identification of yeast has in the past been accomplished by traditional physiological, biochemical and morphological methods, but most of these have lacked speed and accuracy. Bottom-fermenting yeast is often classified as belonging to the genus Saccharomyces (presently classified as Saccharomyces pastorianus), and it has been difficult to differentiate this bottom-fermenting yeast from other Saccharomyces yeast strains which are not bottom-fermenting yeast, such as Saccharomyces cerevisiae, Saccharomyces bayanus and Saccharomyces diastaticus, using the existing traditional methods.
In order to solve this problem, Japanese Patent Application Laid-Open Gazette No. HEI. 11-56366 discloses a method of differentiating brewer's yeast from non-brewer's yeast by using the PCR method for detection of sequence repeats of the FLO1 gene of Saccharomyces. However, it has been reported that the repeating sequences of the FLO1 gene and Lg-FLO1 gene are extremely unstable (Yeast, 10:211-225, 1994, J. Bacteriol. 180(24):6503-6510, 1998), and in some cases the sequence repeats are completely dropped. The method described in Japanese Patent Application Laid-Open Gazette No. HEI. 11-56366 has therefore been associated with the problem whereby even bottom-fermenting yeast is mistakenly identified as wild yeast.